1. Field of the Invention
This invention relates generally to a pad printer, and more particularly concerns improvements to the pad printer structure for maintaining precise timing between a printing plate and a printing pad.
2. Description of Related Art
Generally, the pad printer is the printing instrument that can transfer text, symbol or diagram (hereon, we will call it "text") engraved (or embossed, hereon, we will call it "engraved") in ink coated printing plate to a printing pad. So that in given time, print can go on wood, metal or plastic printing object that ink transfers from the printing pad.
One typical pad printer was described in detail in U.S. Pat. No. 4,905,594, as is illustrated in FIGS. 1 and 2. FIG. 1 is a front view of the typical pad printer, and FIG. 2 is a top view of the typical pad printer. As is shown in FIG. 1 and FIG. 2, a prime pin (14) is cross-connected between two facing support side walls (10), (11) in current pad printer. Side wall (10) is not shown in FIG. 1 for the sake of simplicity. The first lever (12), provided for moving the printing plate mounting member (24) and the printing plate (25) horizontally, and the second lever (13), provided for moving printing pad (27) vertically, are pivotally mounted to the prime pin (14) for rotation. Two cam disks (20), (21) and two supporting rollers (15) and (16) interacting with the cam disks are mounted to the first lever. The two cam disks (20), (21) will be described further below. The support rollers (15), (16) contact the corresponding surfaces ofthe cam disks (20), (21), respectively. As is best seen in FIG. 2, a cam shaft (19) is connected transversely between the supporting side walls (10) and (11), and two facing cam disks (20), (22) are mounted on the cam shaft (19). Therefore, while the cam shaft (19) rotates, the first lever (12) pivots the cam disks (20), (21); and proper selection of shapes of the cam disks (20), (21) permits for the control of the position of the first lever at any given time, and furthermore prevents undesirable movement of the first lever.
In the lower part of the first lever (12), a sliding plate groove (29) is connected to the print moving plate (24) by a bolt. This plate groove (29) provides flexibility required for pivoting movement of the first lever (12) to translate to linear movement of the print moving plate (24).
Additional cam disks (22), (23) are installed to rotate freely in the cam shaft (19). These cam disks (22), (23) interact with the corresponding supporting rollers (17), (18) mounted to the second lever (13). This allows the second lever (13) to be driven in a similar fashion as described for the first lever (12).
As described previously, if the right shape and the position of the cam disk (20-23) are selected, it is possible to precisely fix the interaction between the printing moving plate (24) and the moving phase of the printing pad (27). Therefore, the printing process can be accomplished accurately and smoothly.
Again referring to FIG. 1 and FIG. 2, a printing plate (25) is typically installed in the printing moving plate, and an ink container holding the printing ink (26). A connecting rod (30) is provided between the lever (13) and the printing pad (27), and a guide (28) is preferably provided to allow the printing pad (27) to move vertically.
When electricity is supplied to the prior art pad printer described above, a motor commences to drive the cam disks (20-23) that are connected to the motor by a belt, and the cam disks begin to rotate. When the cam disks (20-23) rotate, the first lever (12) pivots around the prime pin (14) due to interaction between one pair of the cam disks (20), (21) and one pair of the supporting rollers (15), (16), and subsequently, the print moving plate (24) moves horizontally, initially to left. As the print moving plate moves horizontally, ink from the ink container (26) coats the printing plate (25), and the ink coated plate moves horizontally on a bit further to the left.
Simultaneously, the second lever begins to pivot around the prime pin (14) due to interaction between one pair of additional cam disks (22), (23) and another pair of supporting rollers (17), (18). Accordingly, the connecting rod (30) commences to move vertically downward, and, due to the vertical movement of the connecting rod (30), the printing pad (27) connected to the rod also moves downward. Subsequently, the printing pad precisely contacts the printing plate (25), as is depicted in phantom with a dotted line, and ink coating the printing plate (25) is therefore transferred to the printing pad (27). At this point, the printing plate (25) moves horizontally to the right, while the printing pad (27) moves downward a certain further distance, and then an imprint is made on a printing object disposed under the printing pad.
After printing on the object is completed, the printing pad (27) is restored to its original position. Serial movement as described above can be easily accomplished depending on the shape and fixing position of the cam disks (20-23).
In prior art pad printer described above, two each of the sets of cam disks and the supporting rollers are required to move the printing plate horizontally, and another two each of the sets of cam disks and the supporting rollers are required to move the printing pad, leading to high manufacturing costs and excessive manufacturing time. Moreover, the volume and weight of the printing pad machine are increased, and printing position shifting problems can arise as a result of loosening of the axial connection of the cam disks to the prime pin after long usage, which can also result in a phase shift between the print moving plate and the printing pad.